FIG. 4 shows a partial sectional view of a conventional speaker, which comprises the following elements:                magnetic circuit 1A;        voice coil unit 2A movably placed on magnetic circuit 1A;        diaphragm 3A of which inner rim is coupled to voice coil unit 2A;        edge 4A with which an outer rim of diaphragm 3A is coupled to frame 5A; and        suspension holder 6A and edge 7A with both of which a rear face of diaphragm 3A is coupled to frame 5A.Edge 4A and edge 7A protrude oppositely to each other, so that vertical excursion of diaphragm 3A becomes symmetric with respect to a horizontal axis in FIG. 4, thereby reducing distortion of the speaker.        
Such a conventional speaker as discussed above is disclosed in, e.g. Unexamined Japanese Patent Publication No. 2004-7332 referred to as cited reference 1.
The foregoing conventional speaker, however, employs suspension holder 6A which firmly holds diaphragm 3A, so that the weight of the speaker excursion parts becomes heavy. The heavy weight does not matter to a woofer to which a large amount of output is applied, but it matters to a full-range and a mid-range speaker because the heavy excursion parts weight lowers the driving efficiency.